1. Field of the Invention
The present invention relates to an improvement of the carcass structure of a radial tire used for light trucks as well as heavy duty vehicles such as trucks, buses and so forth.
2. Prior Art
A radial tire is superior in wear resistance and low rolling resistance and has been often used for light trucks or heavy duty vehicles.
There have been used some carcass structures, for example, (1) a plurality of carcass plies being turned up around a bead wire from the inside to the outside; (2) some carcass plies (inner plies) being turned up around a bead wire from the inside to the outside and remaining plies(outer plies) covering the turn-up portions of the inner plies and terminating radially inwardly of the bead wire; and so forth. As being well known, polyester cords have been recommended for carcass cord materials in view of the superiority in rust prevention and strength as well as lightness.
Radial tires either for light trucks or for heavy duty vehicles are comparatively superior in durability because of their good properties in wear resistance and low rolling resistance. In case, however, high heat generation is experienced in tire during consecutive tire running under a heavy load or with frequent braking, organic fiber cords such as polyester cords deteriorate by heat so that there occurred the problems such as deterioration in breaking strength or peeling adhesion as well as remarkable deterioration in durability owing to internal breakage of the cords or occurrence of ply separation.